I have a 96 ZJ 4.0. Bought cheap from a couple in Kentucky while I'm here at Fort Knox. Bought it with 174k, for only $1500. Did tune up, new tires, shocks, brakes w/rotors. At 180k I did a fluid and filter pan change on the Transmission.Since I bought it the transmission had a slight slip here and there, especially when cold, but I drive highway home once a month back north near michigan. Driving that long haul is pretty easy going and not many issues, especially after the long haul, when the tranny is hot, it shift a little easier, but you can tell it is having trouble. I know there are a bunch of "Do not Flush High Mileage" forums, and I understand that. I would like to do a fresh fluid flush without the middleman, doing it myself. I understand that doing a pan drop only does 4-5 quarts most of the time, and that the filter is good for 30k, so I'd like to not drop the pan and get most of the dirty fluid out, put new in. Im using MaxLife DexIII at the moment. Any suggestions on Fluid for high mileage trannys? Whats the process of disconnecting a "hose" and running old fluid out with engine started, few quarts at a time, while shutting down engine and refilling the fluid? I also SeaFoamed my Engine today. Just did the Crankcase and gas, didnt have a buddy to help with the vacuum process. Hope that goes well with my next oil change in about 30-40 miles. *just running it through then doing the change.*

You should be using atf+4 in the Trans. Unless you did a complete flush, which it sounds like you didnt, you will now have a mix of dexiii and atf+4. At this point you will probably have to do the full flush.

Not sure which line to disconnect to flush the entire system, I would assume the return line would be the one you want so you can push all the old fluid out of the system.

Yes you need Dex +4 ...... I'd say take it to a shop an get a full flush .. I like the one done with B&G chemicals ..
and I'd say get the filter changed also ..
... If it had 174000 and never had a flush that's a bunch of mile but if it has 260000 like my haul truck but it has had a fluid change or flush about every 30k. and it has had 2 trans in it. So who knows.

@sebian Do you know where the return line is located? Also, would the mix of DexIII cause the slip? cause its a strange slip, its like it doesnt know when to shift. Thing is, if I know its missing, like its reving high, if right before it shifts, I give it a nudge on the gas, maybe 500rpm push, it will then shift more smoothly when it actually goes to shift. If I do continuous pressure, like an average driver, its like it is shifting kinda late. Im thinking solenoid issue? with that High of miles, would a complete flush be a good answer? The previous owners were the original owners, and they DID NOT TAKE CARE OF HER. Oil was black and thick, Tranny Fluid was black, and the pan had SO many shavings and build up.

@papitt How would a complete fluid exchange be done though without doing a flush? as noted before, what hose would be disconnected to allow drain out of old fluid, which would allow new fluid to be put in.. ?

After doing research, since I do NOT want to do a flush, and I am inexperienced with the Pan and all, I am going to do a siphon trade, take 4 quarts out, put 4 quarts in, through the dipstick port. I'll do it every week for the next month so that in the end I have NEW ATF+4 in my Transmission, and still have 20k left on my Filter.

After doing research, since I do NOT want to do a flush, and I am inexperienced with the Pan and all, I am going to do a siphon trade, take 4 quarts out, put 4 quarts in, through the dipstick port. I'll do it every week for the next month so that in the end I have NEW ATF+4 in my Transmission, and still have 20k left on my Filter.

Went to walmart and got the siphon kit and 2 gallon jugs of water for the old fluid/new fluid, drove back,Checked my fluid in Neutral while running today after a 25 min drive, so it was nice and warm, and it was reading below minimum...checked it 3 times... So I added 2 NEW quarts of ATF+4, drove it for 10 min, and now she sits... I checked it and it is at max right now but with the full fluid circulation, I might need 1 more quart possibly. Thats not good! I drove like 8k since my last pan drop and if we didn't put in enough fluid, talk about OVERHEATING. Great way to ruin the trans... Im hopeful though, I'll check over the next few days and monitor the fluid level. Once I get it to the right level, I will then pull 4 more quarts of old and put in new... the cleaner the fluid the better.

What if when I am about to do the trade of 4 quarts old for 4 new quarts trade... I do the SeaFoam Trans Tune around 50 miles before? that would free up some, and then get it out in the old fluid and putting in new fluid would help...? thoughts?

Just my 2cents I would recommend doing a complete transmission flush, new filter, adjust the bands, and adjust the kickdown cable.
I did so to my Jeep about 10k miles ago (just hit 150k) minus adjusting the bands and it shifts fine, kickdown cable fixed weird shifting points and the flush quickened shifts into gears. Me personally I do not believe in all of this do not flush high mileage transmissions stuff, though I only use AMSOil https://www.amsoil.com/shop/by-produ...?code=ATFQT-EA so that could of made a difference to where I ended up not having problems.

did the pan drop and filter less than 8k ago... why would I do it again when I'd be doing the same thing, pulling oil out and putting in new... this is why i'm using the siphoning technique... and its one thing if a few people say it not to be flushed after a certain point, but when 90% of people both amateurs and vet mechanics all say the same thing about it... yeah, i'll listen.